In photography, a bracketing technique refers to a process of capturing a sequence of images that can be used to generate a high dynamic range (“HDR”) image. Such a sequence of images can be referred to as a bracketed sequence of images or a bracket. In at least one conventional bracketing technique, a bracket is fixed. That is, a predetermined number of images form the bracket, with each image being captured at a different exposure value or EV. An example of a conventional fixed bracket is represented as follows:[n(EV−),EV0,n(EV+)],                where EV0 refers to an image that is captured using an ideal exposure value (EV) given the lighting conditions at hand,        where n refers to a number of stops above or below the EV0 image,        where n(EV−) refers to an underexposed image that is captured at n lower stops than the EV0 image, and        where n(EV+) refers to an overexposed image that is captured at n higher stops than the EV0 image.        
In the conventional fixed bracket shown above, “EV” stands for exposure value and refers to a given exposure level for an image (which may be controlled by one or more settings of a device, such as an imaging device's shutter speed and/or aperture setting). Different images may be captured at different EVs, with a one EV difference (also known as a “stop”) between images equating to a predefined power difference in exposure. Typically, a stop is used to denote a power of two difference between exposures. Thus, changing the exposure value can change an amount of light received for a given image, depending on whether the EV is increased or decreased. For example, one stop doubles or halves the amount of light received for a given image, depending on whether the EV is increased or decreased, respectively.
The “EV0” image in a conventional fixed bracket refers to an image that is captured using an exposure value as determined by an imaging device's exposure algorithm. Generally, the EV0 image is assumed to have the ideal exposure value (EV) given the lighting conditions at hand. The “EV−” image of a fixed bracket refers to an underexposed image that is captured at a lower stop (e.g., 0.5, 1, 2, or 3 stops) than the EV0 image. For example, a “1EV−” image refers to an underexposed image that is captured at one stop below the exposure value of the EV0 image. The “7 EV+” image refers to an overexposed image that is captured at a higher stop (e.g., 0.5, 1, 2, or 3) than the EV0 image. For example, a “2EV+” image refers to an overexposed image that is captured at two stops above the exposure value of the EV0 image.
During HDR image creation, one limitation of fixed brackets is the presence of ghosting artifacts that can appear when objects move, appear, or disappear during the capturing of individual images the bracket. For example, during the shooting of three images that are subsequently used for generating an HDR image, if a person is captured in the first image (but not the second and third images), then the HDR image created from the three images can include a semi-transparent figure of the person over the scene. This unwanted ghosting artifact is also known as a ghost.